only two things i can come up with is 1: make new suspension arms that are wider, you can take your plastic arm to a metal shop and they can cut out some AL ones. dont know how hard it will be to drill holes for the axle pins but its possible.
2: transplant suspension arms from another rc car, like a hpi mt2 or a duratrax evader . any 1/10 scale car of your choice. you will also need to transplant the construction walls and the rear diff case as its often attatched to the construction walls that again holds the suspension arms.The only thing you have to do then is drill new holes in the chassis plate, perhaps you can use some of the excisting holes aswell. think that solution is easier, and you will get a stronger differential gear.
hope any of this could be inspiration to a mean smartech buggy